Anna Soubry has called on Theresa May to not let hard-line Brexiteers to dictate Britain's departure from the EU.
The Tory MP told ITV News that Britain had not voted for an extreme Brexit and that the process should not be led by the likes of Boris Johnson and Jacob Rees-Mogg.
"Who's running our country? It's not 30, 35 hard, ideologically-driven Brexiteers who unfortunately are in my party," she said on Monday.
"That's now how we deliver Brexit. That's not what we voted for."
Her comments came after she demanded the PM "sling out" hard Brexiteers, while also threatening to quit the party.
She told Newsnight: "If it comes to it, I am not going to stay in a party which has been taken over by the likes of Jacob Rees-Mogg and Boris Johnson."
"They are not proper Conservatives. "And if that means leaving the party, form some new alliance, God knows I don't know.
"But we just simply cannot go on like this any longer."
She said: "Something is going to have to give because if it doesn't not only will we get Jacob Rees-Mogg as our prime minister, we will get a devastating hard Brexit which will cause huge damage to our economy for generations to come."
Soubry added: "Unless Theresa stands up and sees off these people she is in real danger of losing huge swathes of not just the parliamentary party but the Conservative Party."
In response, Tory former chancellor Lord Lamont said: "I think that's quite ridiculous frankly. I don't want to be rude about Anna Soubry, but I think she does sometimes tend to go over the top."
The comments came as May's Brexit "war cabinet" is due to meet on Wednesday and Thursday to continue discussions on the "end state" relationship which the UK will seek with its former EU partners.
Meanwhile, it was reported the UK could have to accept nearly 40 EU directives during a two year transition period.
Leaked Whitehall analysis revealed Britain may have to adopt measures including households having four different recycle bins, according to The Daily Telegraph.
Other directives could "enable Brussels to mount a massive raid on the City of London and bind the UK to renewable and energy efficiency targets for up to a decade after leaving the EU", the newspaper said.